1. Field of the Invention
The present invention relates to computer data input devices, and more particularly, to a stylus pointer for indicating positions over a detection tablet surface which can be coupled to a computer for inputting data represented by the position or movement of the stylus.
2. Art Background
As the computer revolution has progressed, the familiar form of the machine and the man-machine interface has continued to evolve. Where once punch cards and tape readers, having to be shared by many users, were the dominant interface, today the keyboard interface has become pervasive. The common scheme of a box and keyboard has today become inadequate for many situations. As the drums of time continue beating, the ubiquitous keyboard has reached its limitations.
The advent of advanced semiconductor technologies has resulted in computers becoming smaller and easily transportable. Today, portable laptop computers which utilize small keyboards are nearly as common as desktop computers were just a few years ago. The next step in the downsizing revolution is now upon us. Handheld computers have become so small that the standard keyboard interface is no longer practical or, in many cases, even necessary. The greater computing power of the new machines provides an opportunity for programs and even operating systems to be capable of interpreting written symbols. These small machines are usually provided with flat screens composed of liquid crystal display elements. The flat displays provide an obvious writing tablet-type surface. The logical complement to this is an electronic pen with which to convey inputs to the computers. Even with conventional desktop computers, it is frequently desirable to have the use of a pen-type input.
Tablet and stylus input devices themselves are not new. U.S. Pat. No. 3,838,212 discloses a pen-style input device. The pen is connected to the rest of the hardware by a wire or tether down which a trigger pulse is sent. The trigger pulse causes the pen device to generate a spark gap which creates a shock wave. The leading edge of the shock wave is detected by microphones mounted around the detecting area. The trigger signal is also used as a timing reference for determining the time of travel of the shock wave. The drawbacks of this system are that the wire is required so that the same trigger signal may be used for igniting the spark gap and timing the wave front travel. Another significant disadvantage to such a system is that a spark gap creates audible noise which can be annoying to people in the vicinity. Two such devices near each other may easily interfere. Further, by detecting only the leading edge of the sound wave, the device is likely to be severely susceptible to other extraneous noises.
Other prior art systems suffer many limitations; they are not always accurate, they may have to be connected by a wire, and they may be extremely susceptible to external noises or vibrations. Thus, it would be desirable to provide a stylus and tablet-type interface for computers in which a wireless pen may be used, is accurate and does not suffer from excess external noise and vibration problems.